Many industrial and municipal fluid treatment and distribution systems, as well as small fluid systems such as ice machines, water coolers, fruit juice dispensers, and soft drink machines, are "enclosed fluid systems" having continuous or intermittent fluid flow. The term "enclosed fluid system " as used herein is defined as a system in which fluid is stagnant in at least one portion of the total system and in which there is an intermittent or continuous flow of fluid through the system. Such a system includes distribution piping, storage vessels, metering systems, valves, fittings and fitting accessories, attachments, filter housings, and treatment devices that provide locations where stagnant fluid may reside and where nutrients are available for the growth of microorganisms. The term "fluid" as used herein means liquids such as water, water-oil emulsion, sugar syrups, liquid components, fruit juices, beer, wine, ketchup, molasses. In rare cases, the fluid system may be non-aqueous in nature such as saturated or unsaturated partially hydrogenated oils, alcohols, and wines. In any event, the enclosed systems contain a fluid that is subject to the formation of a biofilm.
The unchecked growth of microorganisms in a fluid system leads to the formation of a biofilm within the system. Biofilm is a conglomerate of microorganisms, such as bacteria, fungi and algae, that are held together, in part, by a sticky substance called exopolysaccharide. Bacteria produce exopolysaccharide, or slime, after attachment of the bacteria to a surface within the fluid system. This slime may be 100 or more times the mass of bacterial cells and helps to anchor and protect microorganisms against disinfecting treatments and allow them to proliferate. Microorganisms protected by the biofilm are resistant to disinfection and enter into the fluid, either continuously or intermittently, as the biofilm sloughs off because of the fluid flow or other mechanical perturbances. Thus, biofilm acts as a major source of microorganism contamination in fluid systems. In many municipal water treatment and distribution systems, the formation of a downstream biofilm negates any upstream treatment of water that attempted to remove the heterotrophic or infectious microorganisms.
Typically, an enclosed fluid system having continuous or intermittent fluid flow is constructed using plastic components. For example, tubing and piping may be made from polyolefin, polyvinylidene fluoride, polyvinyl chloride, ethylene vinyl acetate and polyurethane. Tubing or piping made from polyvinylidene fluoride and polyvinyl chloride are commonly used in the transportation and production of high purity water for the pharmaceutical and electronic industries. For example, tubing made from polyvinyl chloride and polyurethane is used in dental chairs to transport water to the patient during dental procedures. Tubing made singly or coextruded with silicone polymers, polyvinyl chloride/nitrile, polyethylene, chlorobutyl, styrene butadiene rubber, nylon or vinyl acetate are used in food and soft drink dispensing machines.
Numerous plastic polymers and copolymers may be used in these enclosed systems, including among others: epoxies, polyethylene, polyurethane, polypropylene, polyvinyl chloride, acrylonitrile butadiene styrene, polystyrene, polycarbonate, polyvinylidene fluoride, polyacrylate, polymethyl methacrylate, isoprene, styrene butadiene rubber, butyl rubber, polyurethane, silicone, polybutylene, polybutylene terephthalate, polyether sulfone, polyphenyllenoxide, polyphenylene ether, polyphenylene sulfide, polyphtatamide, polysulphene, polyester, nylons, fluoropolymers, and other combinations of polymers. Various copolymers as well as physical combinations of the aforementioned polymers and their alloys are also used in enclosed systems. All of the aforementioned plastic polymers, copolymers and combinations thereof are susceptible to formation of biofilms.
Because many enclosed fluid systems require fluid with particular characteristics, for example cold water from a water cooler, incorporation of a fluid storage chamber is often necessary for the enclosed fluid system. Often these fluid storage chambers are made of the aforementioned plastics. However, enclosed systems may also include metallic based containers, transportation systems or devices. These metallic based containers, transportation systems or devices are typically either powder coated with one or more of the above polymeric substances, such as shown in U.S. Pat. No. 5,238,749, or lined with polymeric substances. For example, pressurized or un-pressurized water storage tanks are often used with wells, hot water heaters and reverse osmosis devices. Pressurized tanks commonly have a flexible butyl rubber or polyurethane diaphragm that is coupled with a plastic liner which together are enclosed in a steel tank. The steel tank is provided with inlet and outlet connections for the flow of water into and out of the tank. The space above the diaphragm is pressurized so that a constant flow of water is afforded regardless of the line pressure. While the predominant fluid transported and contained by enclosed fluid systems is water, it should be understood that enclosed fluid systems may be utilized with other water miscible solvents or oil based emulsions. In rare cases, the fluid system could be non-aqueous in nature, such as saturated or unsaturated, partially hydrogenated oils, alcohols and wines, and food slurries. The major consideration is that the enclosed fluid systems containing any fluid are subject to the formation of biofilm or susceptible to contamination by microorganisms.
What is therefore needed is an enclosed fluid system having continuous or intermittent fluid flow that is resistant to contamination by microorganisms. More particularly, a need exists for an enclosed fluid system that is resistant to contamination by microorganisms throughout the system including the fluid input member, the fluid circulation members, fluid storage members and the fluid exit member. Further needed is an enclosed fluid system that is resistant to biofilm formation for the production and transportation of high purity water in pharmaceutical and electronic applications.